As soon as a chicken stops eating you know you have a problem. Also, if you see any sign of illness it's probably more severe than you think. Chickens are prey animals and they don't show weakness until they are very sick. I have a FAQ about what to do when you think your chicken is sick. http://www.hencam.com/henblog/diagnosing-a-sick-chicken/

Always isolate and evaluate. What the manure looks like is one of the best clues to what is going on. So, keeping the hen separate and seeing what goes in and what goes out is essential.

Your hen is very ill. Respiratory distress is sometimes, but not always due to a bacterial or viral infection in the lungs - BUT it can also be a symptom of a hen filled with infected fluids from cancer or peritonitis. You could try antibiotics, warmth, quiet and TLC. Good luck!